Niobium phosphates as new highly selective catalysts for the oxidative dehydrogenation of ethane

Several niobium phosphate phases have been prepared, fully characterized and tested as catalysts for the selective oxidation of ethane to ethylene. Three distinct niobium phosphate catalysts were prepared, and each was comprised predominantly of a different bulk phase, namely Nb2P4O15, NbOPO4 and Nb1.91P2.82O12. All of the niobium phosphate catalysts showed high selectivity towards ethylene, but the best catalyst was Nb1.91P2.82O12, which was produced from the reduction of niobium oxide phosphate (NbOPO4) by hydrogen. It was particularly selective for ethylene, giving ca. 95% selectivity at 5% conversion, decreasing to ca. 90% at 15% conversion, and only produced low levels of carbon oxides. It was also determined that the only primary product from ethane oxidation over this catalyst was ethylene. Catalyst activity also increased with time-on-line, and this behaviour was ascribed to an increase of the concentration of the Nb1.91P2.82O12 phase, as partially transformed NbOPO4, formed during preparation, was converted to Nb1.91P2.82O12 during use. Catalysts with predominant phases of Nb2P4O15 and NbOPO4 also showed appreciable activity and selectivities to ethylene with values around 75% and 85% respectively at 5% ethane conversion. The presence of phosphorous is required to achieve high ethylene selectivity, as orthorhombic and monoclinic Nb2O5 catalysts showed similar activity, but displayed selectivities to ethylene that were